Operating Planck

Planck’s distance from L2 is similar to that of the Moon from Earth: the average distance of the satellite from L2 is about 400 000 km and one full orbit will take six months to complete.

Because of this large orbit, Planck’s distance to Earth will vary between 1.4 and 1.6 million km. As orbits around L2 are unstable and subtle disturbances will cause the satellite to drift away, Planck will have to perform small orbit correction manoeuvres every month.

During the routine phase, Planck is being operated by the Flight Control Team at the Mission Operations Centre (MOC) at ESA’s European Space Operations Centre (ESOC), Darmstadt, Germany.

The team maintains all necessary contact with Planck using ESA’s New Norcia and Cebreros deep space antennas. The team is also responsible for the health and safety of the spacecraft. From its orbit around L2, it takes about 10 seconds for Planck to communicate with Earth (two-way signal travel time).

The satellite carries out science observations continuously, and the data collected are recorded on board. Planck communicates with Earth for about three hours each day, during which time the team downloads the acquired data and uploads new commands for execution on the following day.

Planck scanning the sky

The Planck science office, located at ESA’s European Space Astronomy Centre (ESAC), Spain, chooses the planned pointings for the spacecraft that make up the sky survey. These inputs are then translated into a schedule of observations which is used to produce the mission operations timeline.

The science office also collects the daily and weekly reports that the instrument teams produce concerning the quality of the science data acquired, in order to track the progress of the survey.

Science data are downloaded to the Estrack receiving station on Earth at a rate of 1.5 Mbits/s and routed to the MOC at ESOC. From there, the data are sent to the instrument data processing centres, where they are processed and analysed. The relevant satellite and scientific data are also sent to the instrument operations centres where they are used to monitor and optimise instrument performance.

The data processing centre and the instrument operations centre for the HFI are located at the Institut d’Astrophysique de Paris, France, and Institut d’Astrophysique Spatiale d’Orsay, France, respectively, whereas those for the LFI are located at the Osservatorio Astronomico di Trieste, Italy.

The nominal mission operation will last 15 months to carry out two full surveys of the sky. All scientific data will be archived at ESAC and made available to the worldwide astronomy community two years after the end of the nominal mission.